1. Field of the Invention
The present invention relates to a mounting structure for a lens array unit used in an image reading device.
2. Description of the Related Art
Some image reading devices according to the related art, such as scanners, are known to use erecting equal-magnification optical systems. The use of erecting equal-magnification optical systems allows reducing the size of devices better than reduction optical systems. In the case of image reading devices, an erecting equal-magnification optical system comprises a line light source, an erecting equal-magnification lens array, and a line image sensor.
A rod lens array capable of forming an erect equal-magnification image is conventionally used as an erecting equal-magnification lens array in an erecting equal-magnification optical system. Recently, there is proposed a lens array unit formed as a stack of a plurality of transparent lens array plates built such that the optical axes of individual convex lenses are aligned, where each transparent lens array plate includes a systematic arrangement of micro-convex lenses on both planes (see, for example, patent document No. 1). Since a lens array unit such as this comprises a stack of lens array plates formed by, for example, injection molding, an erecting equal-magnification lens arrays can be manufactured at a relatively low cost.    [patent document No. 1] JP 2001-352429
Methods for mounting a lens array unit to the housing of an image reading device include using an adhesive to secure a unit in a recess formed at a predetermined position of the housing.
However, securing of a unit by using an adhesive requires maintaining the lens array unit stationary during the process of securing, by using a dedicated jig or the like. Such an approach is disadvantageous because of poor efficiency of assembly. A slight displacement of the unit maintained by a jig or foreign materials sandwiched between the housing and the lens unit will cause a part of the lens unit to be elevated from the housing along the main scanning direction, causing the optical axis of the lens array unit to be inclined.